1. Field of the Invention
This invention relates to a method for forming a thin film, particularly to a method for forming a thin film suitable for optical sensors, emission materials, electronic materials.
2. Background of the Invention
So far, a sol-gel method, a CVD method or a PVD method is employed as a thin film-forming method. These methods require multistage process including a heating process, a high vacuum condition, or a high energy condition accompanied with a substrate-heating process or a plasma-generating process. Therefore, those methods require large scale and complicate apparatus, resulting in large cost and complicate operationality in use.
Moreover, the above high energy condition runs counter to global environmental protection, resource saving and energy saving. Therefore, a new thin film-forming method without the above high energy condition has been desired.
It is an object of the present invention to provide a new thin film-forming method not including a high energy condition due to firing, heating or plasma generation.
This invention relates to a method for forming a thin film comprising the steps of:
preparing a reactive solution incorporating. the components of the thin film,
charging the reactive solution into a minute nozzle, and
spraying the liquid drops of the reactive solution from the minute nozzle onto a substrate, and thus, synthesizing the components to form the thin film on the substrate.
The inventors related to the present invention have been intensely studied for developing a new thin film-forming method not including a high energy process. As a result, they have found out surprisingly that when a reactive solution incorporating components of a desired thin film is directly sprayed on a substrate from a minute nozzle, the desired compound thin film including the components is synthesized directly on the substrate at room temperature. Then, it has been turned out that the compound thin film has well crystallinity.
Compound particles are synthesized in the substrate through reaction, precipitation and/or drying of the solution in a small amount sprayed on the substrate and they stick to the substrate without any particular pastes or post treatments like firings.
In this regard, the solvent is not restricted but aqueous solvents including organic solvents are preferable because they are vaporable easily.
Since the minute nozzle may be attached to an ink-jet printer, it can be moved relatively for the substrate on which the compound thin film is formed. As a result, the reactive solution can be sprayed on any part of the substrate, and thus, the compound thin film can be easily formed in a linear shape, a dot-shape, a plane-shape or a three dimensional shape.
In a preferred embodiment of the present invention, the substrate is composed of a porous material such as a paper (a filter paper, a glossy paper or a fine paper) or a cloth (a cotton cloth or a polyester cloth), and then, at least one blended solution to constitute the reactive solution is infiltrated into the substrate. Thereafter, the other blended solutions are sprayed onto the substrate from the minute nozzle. As a result, the infiltrated blended solution is reacted with the sprayed blended solution, and thus, the compound thin film, which is composed of the components of the above blended solutions, is synthesized directly on the substrate.
If at least one blended solution to constitute the reactive solution is infiltrated into the porous substrate in advance, the number of the blended solutions to be sprayed from the minute nozzle can be reduced. Therefore, in the synthesis of the above compound thin film on the substrate, the pattern controlling can be easily performed and thus, the compound thin film can be easily formed in various shapes such as linear shape, dot shape, plane shape or three-dimensional shape. Moreover, the adhesion strength between the compound thin film and the substrate can be enhanced by the indefinite anchor effect.